A conventional method for applying material to the surface of a substrate is screen printing. Screen printing consists of forcing a type of material, in the form of a paste, through a mesh screen, parts of which have been blocked, thereby applying the paste to a substrate in a desired pattern. Screen printing allows a layer of material to be deposited onto a smooth substrate surface in a fast and economical fashion. One problem associated with screen printing methods is thickness control. At the present time, screen printing is not used to apply thick layers (in the range of between 8 to 12 mils) of emissive material, such as phosphor or other latent illuminance materials, to a substrate.
Current methods used for depositing emissive material onto a substrate include flexographic printing and pad printing. Flexographic printing involves applying a material, such as an ink, to a plate using a roller that is engraved with a pattern to determine the amount of ink to be delivered to a substrate. The plate then comes in contact with the material and transfers to the ink image onto the substrate. Pad printing involves etching depressions into a flat plate or printing block and then filling the plate or block with ink. The ink is picked up by a silicone pad, which transfers the ink to a substrate. However, such methods are limited to depositing a thin layer (about 2 mils or less) of emissive material onto substrate and are incapable of depositing a thicker layer (in the range of between 8 to 12 mils) of emissive material onto a substrate without producing spotty, inconsistent results.
Emissive material (also referred to herein as latent illuminance material) may be applied to an object such as a data storage cartridge as an identification/authentication tag or marker. After a tag containing the emissive material has been illuminated, it emits light having certain characteristics, such as spectral characteristics or decay time, that can be detected and analyzed to determine the identity/authenticity of the tag, and thus, the object attached to the tag. This technique is described in a co-pending application titled "Latent Illuminance Discrimination Marker For Data Storage Cartridges", Ser. No. 09/161,007, filed Sep. 25, 1998 commonly assigned, and incorporated herein by reference. The emissive material that is applied to a data storage cartridge desirably emits a significant amount of irradiance in order for the detector or reader in the drive to provide accurate detection results. To successfully achieve emission of a significant amount of irradiance, the emissive material is preferably applied in a thick layer (at least 8 to 12 mils) to the tag or directly on the object being identified. The current methods used to apply emissive material do not allow for the continuous, single pass application of such a thick layer of emissive material.
Moreover, the type of emissive material that is normally deposited onto a substrate is electro-luminescent material (i.e., a material that is electrically excitable). However, the type of emissive material that provides the desirably accurate detection results for the technique described above in co-pending application, Ser. No. 09/161,007, is a luminescent phosphor (i.e., a material that is excited by light), such as an aggregate particle phosphor. Luminescent phosphor has a larger particle size (between about 0.5 and 6 mils) than that of electro-luminescent material. The current methods used to apply luminescent material do not allow for the application of a layer of luminescent material with such a large particle size.
Accordingly, it is desirable to overcome the above listed limitations on the thickness and particle size of a layer of emissive material that can be applied to a substrate in a continuous, single pass manner.